1. Field of the Invention
The invention relates to a temperature sensing device for measuring the temperature of working gas in the heater tubes of a hot gas engine heater head. More particularly, the invention relates to a thermo-couple placed in but isolated from the working gas for measuring its temperature while reducing error caused by exposure to the working gas.
2. Description of the Prior Art
Heater heads of hot gas engines, such as the Stirling cycle engine heater head disclosed in U.S. Pat. No. 4,069,670, are provided with temperature sensing devices to measure the temperature of the hot working gas in the heater head or of the wall of the heater head. The temperature of the working gas in the heat exchange pipes or heater pipes of the heater head is measured to provide a parameter for control of other engine parameters such as air/fuel ratio or power output.
Thermo-couples are the most commonly used temperature sensing devices, but their use is restricted to avoid error caused by the environment in which they are placed. For example, thermo-couples have been placed within one or more of the heater tubes to measure the working gas temperature, as disclosed in U.S. Pat. No. 3,835,648. The drawback of such a location for a thermo-couple is the detrimental effect the working gas may have on the thermo-couple. A thermo-couple of the type that measures actual temperature range is adversely influenced by hydrogen, a common element in the working gas of hot gas engines.
The thermo-couple, however, cannot be used outside the heat exchange tubes or heater tubes without protection because of the combustion gases. Providing protection for the thermo-couple may induce an error in temperature measurement.
Furthermore, the temperature signal conduction wire leading to the thermo-couple must be protected from extreme temperatures and, therefore, cannot pass through the combustion gases to reach thermo-couples mounted outside the heater tubes.
The present invention overcomes the disadvantages of the prior art by providing a temperature sensing device which is isolated from gases and extreme temperatures beyond those intended to be sensed, which may adversely effect its reliability or accuracy.